The present disclosure relates to semiconductor device manufacturing, and more particularly to methods for controlled removal of a semiconductor device layer from a base substrate in which, after the removal of the semiconductor device layer from the base substrate, the base substrate has a planar surface and thus can be reused.
Devices that can be produced in thin-film form have three clear advantages over their bulk counterparts. First, by virtue of less material used, thin-film devices ameliorate the materials cost associated with device production. Second, low device weight is a definite advantage that motivates industrial-level effort for a wide range of thin-film applications. Third, if dimensions are small enough, devices can exhibit mechanical flexibility in their thin-film form. Furthermore, if a device layer is removed from a substrate that can be reused, additional fabrication cost reduction can be achieved.
Efforts to (i) create thin-film substrates from bulk materials (i.e., semiconductors) and (ii) form thin-film device layers by removing device layers from the underlying bulk substrates on which they were formed are ongoing. The controlled surface layer removal required for such applications has been successfully demonstrated using a process known as spalling; see U.S. Patent Application No. 2010/0311250 to Bedell et al. Spalling includes depositing a stressor layer on a base substrate, placing an optional handle substrate on the stressor layer, and inducing a crack and its propagation below the base substrate/stressor interface. This process, which is performed at room temperature, removes a thin layer of the base substrate below the stressor layer. By thin, it is meant that the layer thickness is typically less than 100 microns, with a layer thickness of less than 50 microns being more typical.
The depth of at which the crack propagates is dictated by the thickness of the stressor layer, the inherent tensile stress of the stressor layer, and the fracture toughness of the base substrate being exfoliated (spalled). However, control of the initiation of the release layer process (crack initiation and propagation) is not easy. Moreover, the spalled surface is usually not flat and hence, the base substrate cannot be reused, which increases manufacturing cost.